Heretofore, various types of agricultural-chemical formulations such as dusts, granules, wettable powders, water-dispersible particulates, liquids, aqueous suspensions, emulsifiable concentrates, and the like have been known. Of these agricultural-chemical formulations, water-dispersible particulates are easy for users to handle since they do not powder during use thereof and therefore users would be exposed little to the agricultural-chemical ingredient and since they are easy to meter. Accordingly, forms of recent agricultural-chemical formulations tend to be changed from wettable powders to water-dispersible particulates.
In general water-dispersible particulates should easily disperse in water, and for this purpose they should be produced by a method in which granulation is not accompanied by application of pressure and the resulting granules are free from a consolidated structure. Such methods include a so-called fluidized-bed granulation method where a powdery mixture of an agricultural-chemical active ingredient, a surfactant and an extender or the like is fluidized in a layer into which hot air is pumped, and an aqueous solution containing a binder is sprayed thereon to make the powdery particles aggregate together thereby forming granules; and a so-called stirring granulation method where an aqueous solution containing a binder is sprayed on a powdery mixture of an agricultural-chemical active ingredient, a surfactant and an extender or the like kept stirred at high speed to make the powdery particles aggregate together thereby forming granules (Non-Patent Documents 1 and 2).
In these methods, however, the granules produced have a broad particle size distribution and sieving results in a low production yield with respect to a necessary particle size. In addition, since the granulation is carried out as a batch process, the amount of the granules to be produced per unit time is small. Therefore, the methods are substantially unsuitable for industrial production of agricultural chemicals.
On the other hand, as a granulation method that secures high producibility of agricultural-chemical formulations, there is a so-called extrusion granulation method where an agricultural-chemical active ingredient, a surfactant and an extender or the like are kneaded with water, and extruded through pores formed in a screen to give columnar granules (Non-Patent Document 1). In this method, a high pressure is given to extrude the mixture through the pores and, as a result, the formed granules have a consolidated structure with poor water-dispersibility. In this connection, while the water-dispersibility could be improved by reducing the diameter of the pores to have smaller granules, the pressure to be imparted to the screen may increase with reduction in the diameter of the pores and cause increased fragility of the screen thereby precluding the granulation itself.
Also, as a method for producing a granular agricultural-chemical composition having improved water-dispersibility and suspensibility of agricultural-chemical ingredient, there is a method in which a mixture containing an agricultural-chemical active ingredient and a surfactant is kneaded with water, and the kneaded mixture is pulverized to have a predetermined particle size and dried, or the kneaded mixture is dried and made to have a predetermined particle size (Patent Document 1). In this method, although the resulting granules are not in a consolidated state and have good water-dispersibility, the step of pulverizing the kneaded mixture may cause problems. Specifically, in the case where the kneaded mixture before dried is pulverized, the mixture significantly adheres to the pulverizer because of water contained in the mixture. On the other hand, the kneaded mixture which is dried before the pulverization is extremely brittle and the size distribution of the pulverized particles is large, therefore the production yield of the granular agricultural-chemical composition having the intended particle size is extremely low.    Patent Document 1: JP-A 2001-288004    Non-Patent Document 1: Handbook of Granulation Technology, edited by the Association of Power Process Industry and Engineering, Japan    Non-Patent Document 2: Granulation Manual, edited by the Association of Power Process Industry and Engineering, Japan